Unfinished let error if a line of string interpolation starts with a format instructions inside of a module

[MangelMaxime]

Please provide a succinct description of the issue.

Repro steps

Provide the steps required to reproduce the problem:

module T =

    let evalute path =
        if true then
            let errors = ""

            let msg =
                $"""An error occured while loading {path}
Original error:
%s{errors}"""

            printfn "%s" msg

If I add at least 3 spaces at the beginning of the line %s{errors}""" then the error goes away.

There is no error if the function is not under a module:

Expected behavior

No error should be reported.

Actual behavior

The is a compilation error.

Known workarounds

Use string concatenation instead of string interpolation.

Related information

Provide any related information (optional):

• Operating system: Windows
• .NET Runtime kind (.NET Core, .NET Framework, Mono): .NET Code 6.0.302
• Editing Tools (e.g. Visual Studio Version, Visual Studio) VSCode + Ionide

[vzarytovskii]

@MangelMaxime does this only show in VSCode, or VS too?
cc @baronfel

[MangelMaxime]

@vzarytovskii

The error happens in Ionide, FSI, dotnet build too.

The code I provided in the issue should serve as a reproduction I believe.

[dsyme]

This is a non-trivial bug in the lexfilter, when processing the tokens of multi-line interpolated strings - it is interpreting one of the tokens as being offside of the let.

[dsyme]

I assume the fix will be to push a new LexFilter context for the duration of the processing of the let. However it's not going to be a simple fix.